1. Field of the Invention
The present invention relates to a method of visual tracking with use of color. More particularly, the invention relates to a visual target tracking method applicable for various fields in such techniques as correcting important parts of recorded images for broadcasting stations, tracking human faces in unmanned monitoring systems, tracking speakers for remote conferences, or remote conversation through communication networks, setting face contours for face recognition in security systems, tracking of a specified target, and so forth.
The need for tracking or recognizing a target having a specific color is increased in various application fields like broadcasting, unmanned monitoring systems, security systems, remote conferencing through communication networks, control of unmanned flying objects, unmanned docking systems, etc. Considering the fact that a majority of information human beings obtain is through visual means, visual tracking techniques are expected to further expand their application fields in the future.
2. Description of the Related Art
In conventional visual tracking techniques using color information, colors of the target have been represented by color models known to be robust with respect to illumination changes, such as in normalized Red-Green-Blue (R-G-B) space or Hue-Saturation-Intensity (H-S-I) space.
However, these color models well accommodate uniform changes of illumination, but show limitations in cases where the brightness of the target changes irregularly due to angle changes between light source and target or the brightness changes abruptly.
For example, when a man is walking through a gallery whose ceiling is equipped with fluorescent lights at uniform intervals, the relative position of the immediately affecting fluorescent light relative to the man keeps changing and, therefore, the brightness of the man's face keeps changing. And depending on the direction the man is moving, it often probable that one side of the face gets darker while the other side gets lighter. Moreover, the surface reflectiveness of a human face is hardly uniform due to secretion of sweat and it is extremely unlikely for the whole face to have uniform illumination changes.
In other words, since color distribution changes as illumination intensity varies, the conventional visual tracking techniques have problems in using a color model normalized and set-up for uniform illumination changes.